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Night terrors

27 June 1998

By Alison Motluk

DO axe-wielding madmen make regular appearances in your dreams? If so blame
your genes, say Finnish scientists. They have found that identical twins are
twice as likely to share the trait of having frequent nightmares as nonidentical
twins. The work has also confirmed a strong link between nightmares and mental
illness.

Nightmares raise your pulse rate and step up metabolism in the brain. The
frequency of your nightmares tends to stay roughly the same from childhood
through middle age, with some people suffering three or four nightmares a
week.

Christer Hublin of the University of Helsinki and his colleagues looked at
nightmare frequencies in 2276 pairs of identical twins and 4172 pairs of
nonidentical twins. They found that if one of a pair of identical twins reported
frequent nightmares—that is, three or more nightmares per week—there
was a 45 per cent chance that the other twin would share the same trait. With
nonidentical twins, there was only a 20 per cent chance. “Your genetic
constitution may make you more liable to nightmares,” says Hublin.

The findings also link frequent nightmares with mental illness. Examination
of the volunteers’ medical records showed that people who have frequent
nightmares are 15 per cent more likely to be hospitalised at least once in their
lifetime for mental illness, the researchers reported last week at a meeting on
sleep research in New Orleans. “We don’t know if it’s causative or
co-occurring,” says Hublin.

Markku Partinen, another member of the team, notes that people with
depression and schizophrenia report more nightmares than healthy people. He
speculates that nightmares may be due to abnormal activity in the limbic system,
the part of the brain that deals with emotions.